The present invention relates to an internal combustion engine controller for driving a load by using a high voltage obtained by boosting a battery voltage, and more particularly to an internal combustion engine controller suitable for driving a cylinder direct injection type injector.
For the purposes of improving a fuel consumption and an output, an injector for directly injecting fuel in a cylinder is used with an internal combustion engine controller of an engine using gasoline, gas oil or the like as its fuel, such as those of automobiles, auto-bikes, agricultural tractors, machine tools, and marine vessels. An injector of this type is called “cylinder direct injection type injector, “direct injector”, or simply “DI”.
As compared to a premix type engine which is the main stream of gasoline engines, forms mixture gas of air and fuel in advance and introduces the mixture gas into a cylinder, an engine utilizing a cylinder direct injection type injector is required to provide larger energy when opening a valve of the injector, because the engine uses fuel pressurized to a high pressure. It is also necessary to supply a large current to the injector in a short time, in order to improve controllability and realize high speed.
Most of conventional internal combustion engine controllers controlling a cylinder direct injection type injector are provided with a voltage booster circuit for boosting a battery voltage to a higher voltage and making the voltage boosted by the voltage booster circuit increase an exciting current to the injector in a short time.
A drive current waveform for a typical direct injector uses a boosted voltage during a peak current exciting period at an initial exciting stage to increase an injector current to a predetermined peak stop current in a short time. This peak current is about five to ten times an injector current of the premix type engine which introduces a mixture gas of fuel and air into the cylinder.
After the peak current exciting period, an energy supply source for the injector transits from the boosted voltage to the battery power source. The injector current transits, via a first hold current controlled by a first hold stop current about a half to one thirds of the peak current, to a second hold current controlled by a second hold stop current about two thirds to a half of the second hold current. The peak current and first hold current open the valve of the injector and inject the fuel into the cylinder.
In order to close the valve of the injector immediately after injection, it is necessary to complete an exciting current reduction period of the injector exciting current in a short time to cut off the injector current.
However, large energy is accumulated in the injector because of a flow of the injector current. In order to cut off the injector current, it is necessary to extinguish this energy from the injector. In order to realize this in a short time during the exciting current reduction period, various methods have been adopted including a method of converting energy into thermal energy by driver elements of a driver circuit for driving the injector current by utilizing the Zener diode effects and a method of regenerating the injector current to a voltage booster capacitor of the voltage booster circuit for accumulating a boosted voltage.
With the former method, although the driver circuit can be simplified, this method is not suitable for a large current driver circuit because the injector exciting energy is converted into thermal energy. In contrast, with the latter method, even if a large current is flowed to the injector, heat generation of the driver circuit can be suppressed relatively. Therefore, this method is widely used particularly for an engine using a direct injection injector using gas oil (called also common rail engine) and an engine using a direct injection injector using gasoline as fuel (called also DIG or GDI), which require a large exciting current to the engine.
During the period of reducing the injector current, the injector current is reduced in a short time in some cases also during the exciting current reduction period, a peak current reduction period and a first hold current reduction period. Similar to the exciting current reduction period, the operation of the injector driver circuit is performed during these periods by turning off all of a voltage booster side FET, a battery side driver FET and a first downstream side driver FET.